Air sweetening process for naphthas



. 8, 1959 E. J. NlEHAus, JR.. ETAL 2,916,442

AIR SWEETENING PRocEss FOR NAPHTHAS Filed Nov. 14, 1956 v z. OZ-Dn-OI owwww 1v m www r 3 5.5m 9 mmf wm l A a ll. T QQ .3 EXE E .Emw 1v motmz. nn. tmm oN l' Al Al A! Q l.' |v E T N @Mmmm mm oz .596mm $355 op? (wmmzmwommx m T 35.2 om ..mnw mzmmommx of the added inhibitor to convertthe mercaptans to United States Patent O 2,916,442 AlR SWEETENINGPROCESS FOR NAPHTHAS Edward J. Niehaus, Jr., and William H. Gay,Baltimore,

Md., assignors to Esso Research and Engineering Company, a corporationof Delaware Application November 14, 1956, Serial No. 622,110 9 Claims.(Cl. 208-204) This invention concerns an improved process for sweeteningpetroleum distillates. The invention is particularly directed to thesweetening of naphtha derived from catalytic cracking operations. Thesweetening is effected by a novel process in which use is made of anagent that will dissolve in caustic, will absorb oxygen when blown withair and will give up this oxygen when it comes into contact with acracked naphtha, the oxygen then reacting with the mercaptans in thenaphtha to form disuldes.

It is well known in the art of petroleum refining to sweeten sourdistillates such as naphtha, motor fuels and the like, by contactingthem with various reagents such as caustic soda. Such treatment is notentirely satisfactory because not all of the mercaptans that are presentin the petroleum distillates will dissolve in the caustic. It is alsoknown that further removal of the mercaptans can be effected by what isknown as air sweetening wherein the mercaptans are oxidized to formdisuliides which remain in the sweetened distillate.

It is one object of the present invention to provide an improved processfor the air sweetening of petroleum distillates. It is an ladditionalobject of the invention to provide a process wherein thesweeteningproceeds at a faster rate and `at a lower temperature thanwith previously known air sweetening processes.

In accordance with the present invention, a cracked naphtha or similardistillate such as gasoline is rst treated with caustic soda to removehydrogen sulfide and caustic-soluble mercaptans, particularlythiophenols. A small amount of a compound selected from the class ofamines, amides and phenols is then added to the treated naphtha. Sincemost compounds of this class are well known as oxidation inhibitors itis convenient to referto them as inhibitors in the subsequentdiscussion. The naphtha containing the added inhibitor is next contactedwith caustic that has previously been employed for treating raw kerosenedistillate. The naphtha, after separation from kerosene caustic, isplaced in a holding tank or storage vessel for several hours, where thesweetening occurs by action of oxygen on the stored naphtha. Thesweetened' naphtha is then ready for blending into gasoline.

The oxygen is preferably introduced into thev system by saturating thekerosene caustic with air or oxygen prior to contacting the kerosenecaustic with the naphtha. Alternative procedures comprise introducingair or oxygen into the naphtha just prior to contacting the same withthe kerosene caustic or else introducing the air or oxygen intotheholding tank.

The exact function of the kerosene caustic is not completely understoodbut it is believed that certain substances extracted from the keroseneby the caustic used for treating the same act as carriers of oxygenwhich is given up to the naphtha on contact. This oxygen reacts slowlywith the mercaptans in the naphtha in the presence Patented Dec. 8, 1959suldes, thus causing the naphtha to become sweet during its storage inthe holding tank.

The nature of this invention and the manner of its operation will bemore readily understood when reference is made to the accompanyingdrawing in which the single figure diagrammatically illustrates theprocess steps followed in practicing this invention.

Referring now to the drawing in detail, a raw kerosene fraction enteringthrough line 12 is treated in a conventional agitating vessel 11 with acaustic soda solution entering through line 13. Agitation may beeffected by blowing with air entering through line 14 and leavingthrough exit 17. Preferably, the caustic soda is of from l0 to 20 B.strength, and from l to 5 volume percent of caustic based on thekerosene is employed. The mixture is allowed to settle and the treatedkerosene is drawn off through line 15 and sent to storage or to furthertreatment. The caustic from the kerosene treatment is removed throughline 16 and sent to an accumulator 23. f Alternatively, the kerosene maybe treated with caustic by sending the kerosene and caustic throughlines 12a and 13a, respectively, into a line mixer 18 and from therethrough line 19 to a drum settler 20 where separation of caustic fromkerosene may be effected, the kerosene being sent through line 21 tostorage or further treatment and the separated caustic being sentthrough line 22 to the accumulator.

Any entrained kerosene that enters the accumulator will separate out andcan be sent back to the settler 20 by means of line 24. The kerosenespent caustic, which may also be referred to as promoter solution, isdrawn from the bottom of the accumulator, as required, through line 25,and added to the naphtha sweetening system via recycle line 26 whichcarries circulating promoter solution to a saturator tower 28 whereinthe solution is brought into intimate contact with oxygen or anoxygencontaining gas such Ias air which enters the saturator towerthrough line 29. The saturator tower may be a packed tower, a bubble captower, or a similar tower designed for intimate contact between gasesand liquids.

The sour catalytic naphtha that is to be sweetened is given apre-sweetening caustic wash by contacting it with caustic soda in a linemixer 33, the caustic entering through line 35 and the sour naphthaentering through line 34. The concentration of caustic in'this step isnot critical and could range from 5 to 45 B.; preferably a caustic sodaof from l0 to 20 B. is employed. The mixture of naphtha and caustic isconducted through line 37 to =a drum settler 38 where separation ofcaustic and naphtha takes place. Caustic may be recycled to the mixingzone through line 36 and spent caustic may be removed through line 39.The treated naphtha leaves the settling drum through line 40 and isconducted to another line mixer 43, after a small amount of an inhibitorof the type referred to above has been added by means of line 41. Theinhibited naphtha contacts promotor solution from the saturator towerwhich is fed into the mixer through line 32. Preferably the promotersolution is used in the proportion of from about 5 to 20 percent of thenaphtha. The mixture of the naphtha and promoter solution is conductedthrough line 44 into a drum settler 45 where separation of naphtha frompromoter solution occurs, the separated naphtha being then conducted bymeans of line 47 into the holding tank 4S Where the naphtha is storedAfor several hours to complete the sweetening action. The sweetenednaphtha is then removed through line 49.

Promoter solution separated from the naphtha in settling drum 45 is sentback to the recycle surge 27 through line 46. Any entrained naphtha thataccumulates in the recycle surge drum may be pumped to the naphthaholding tank by means of line 63.

It is preferred to saturate the promoter solution with oxygen or air ina saturator tower, as previously described. Alternative methods may beused, however.

'For example, thesaturatortower-may beeliminated'and the promotersolution sent directly'to the mixer 43 by ymeans of lines 5() and 32,-thus bypassing the saturator tower. Air or oxygen is then introducedinto the 'naphtha stream following inhibitor injection, as for example'bymeans of line S1. An alternative method for introducing air is to addthe airor oxygen to the holding tank, as lfor example by means of line52. Also, any combination of the three methods of air Vinjectioncou'ldbe used. However, from the standpoints of safety and effectiveness ofsweetening, it ispreferred'to employ the sat'urator tower.

Although this invention is directed primarily to the "sweetening ofcatalytic naphthas, it is possible to sweeten a mixture of virginnaphtha and catalytic naphtha. In the event vthat virgin naphtha is tobe mixed with the racked naphtha, the sour virgin naphtha is given apresweetening caustic wash in the same manner as in the case of acracked naphtha. Thus, sour virgin naphtha from line 54 is mixed withcaustic soda from line 55 in 'a line mixer 53 and the mixture is sentthroughline 57 to a settling drum 58 wherein separation between causticand naphtha takes place, the pretreated virgin naphtha then beingconducted through line 60 to be admixed with 'the pretreated crackednaphtha in line 40 at or nearthe point of introduction of the throughline 32. As in the promoter solution entering case of the pre-sweeteningyof the cracked naphtha, the caustic separated from the -reaction, areselected from the class consisting of amines,

amides and phenols. Compounds of this class which have been foundeffective in promoting oxidative sweetening include acetamide,n-butyramide, N-butyl benzamide, phenol, beta naphthol, p-amino phenol,the phenylene diamines, crude petroleum phenols, and triethanolamine.The preferred compounds for use in this invention are -the phenylenediamines such as para-phenylene diamine and N,Ndisecbutyl-p-phenylenediamine. In practicing this invention the selectedinhibitor is added to the dis- `tillate being treated in the amount offrom about 0.05

to one pound per thousand gallons of distillate, and.pref erably in therange of from about 0.1 to 0.5 ,poundper thousand gallons.

Although when reference is made to caustic in this disclosure, causticsoda is usually meant, it is tobe understood that the use of alkalimetal hydroxides other than sodium hydroxide, such as potassiumhydroxide, is not precluded. Sodium hydroxide is usually employedbecause of its greater availability and generally llower cost. It is tobe understood that in practicing this invention lthe step of subjectingthe naphtha or gasolineto a pre- 'sweetening caustic wash will benecessary whenever hy- -drogen sulde and/or other acidic materials arepresent that would interfere with or impair the eliiciency of thesubsequent air sweetening steps.

In those instances where it is definitely known that materials'such'ashydro gen suliide which are deleterious to the air sweetening Ymechanismare absent, the pre-sweetening caustic -wash may be dispensed with. Thisstep necessary, however.

will in general be The following examples serve to illustrate theadvantages of this invention:

EXAMPLE 1 A promoter solution was prepared by treating a kerosene from asweet Louisiana mixed crude with one volume percent of 15 B. causticsoda at 110 F. by air blowing in a plant agitator. Two separate samplesof a light catalytic cracked naphtha having an A.P.l. gravity of 67.2and a boiling range of 108 to 340 F. were given a pre-sweetening washwith 10 volume `percent of 15 B. caustic soda. One of the pre-treatedsamples was given a second fresh caustic wash with 10 volumepercent of15 B. caustic. The other pretreated sample was given a ywash with 10volume percent ofthe promoter solution prepared as described. In eachcase a small quantity of N,Ndisec-butyl-p-phenylene diamine was added toeach of the pretreated naphtha samples before the second caustictreatment. The quantity of inhibitor added was equivalent to 0.2 poundper 1000 gallons of naphtha.

After the second treatment, with fresh caustic in the one case land thepromoter solution in the second case, the naphtha samples were separatedfrom the caustic and placed in separate holding tanks where the naphthasamples were held vfor a number of hours at temperatures of from 75 to77 F. In the case of the naphtha given two vfresh caustic washes, an airspace amounting to 50 volume percent of the holding tank was maintained,whereas in thev case of the naphtha treated with the promoter solution,air was excluded from the holding tank and the vapor space was blanketedwith nitrogen. In each `case the naphtha was agitated for one minuteprior to the beginning of the storage period. Samples of the naphthawere taken from each of the storage vessels at periodic intervals todetermine the amount of sweetening that had occurred. Test results arepresented l Milligrams of mercaptan sulfur per milliliter-s of naphtha.

2 10 volume percent of 15 Baume caustic used in each instance.

-It will be noted that in the case in which the promoter solution wasemployed, i.e. the spent caustic from kerosene treatment, the sweeteningwas completed in vless than 18 hours, whereas in the case where freshcaustic was employed in the second caustic wash, the naphtha was stillnot sweet after hours, even though the naphtha in the latter case hadthe advantage of agitation in a tank having a 50 percent air space.

EXAMPLE 2 In a second series of tests, the elect of varyingthe method bywhich air was introduced was determined. Three separate catalyticnaphtha samples were employed, identified as naphthas A, B and C.Naphtha A had an A.P.I. .gravity of 64.4 and a boiling range of 96 'to356 F., naphtha B had an A.P.I. gravity of 67.2 and a boiling range of108 to 340 F, and naphtha C had an A.P.I. gravity of 63.8 and a boilingrange of 100 to 344 F. As in Example 1, each of the naphtha samples wasgiven a pre-sweetening caustic wash with 10 volume percent 'of fresh 15B. caustic. The samel oxidation inhibitor as used in Example 1 was thenadded to each of the samples in a concentration equivalent to 0.2 poundper 1000 gallons of naphtha. Portions of each of the naphthas were thentreated with the same promoter solution as used in Example 1. In somecases the promoter solution was aerated before contacting the naphthaand in other cases it was not.

Also, in some cases an air space was provided in the holding tank inwhich the naphtha was placed after the treatment with the promotersolution and in other cases air was excluded. As in Example l theprogress of the sweetening was followed by the removal of portions ofthenaphtha at periodic intervals, and determinationV of the mercaptannumbers of the samples thus collected. The results obtained arepresented in Table II. The table also contains footnotes indicating theaeration procedure used in each instance.

range of from 96 to 334 lF. was employed. sweetening tests wereconducted with this naphtha alone as well as with mixtures of the virginnaphtha and a sourcatalytic naphtha having an A.P.I. gravity of 63.8andy a boiling range of from 100 to 344 1F. Tests were also conductedwith the sour catalytic naphtha alone. In each instance the naphtha wasgiven a pretreat with l0 volume percent of 15 B. caustic, after whichthe phenylene diamine inhibitor employed in the previous examples wasadded to each naphtha sample, in the same concentration as in thoseexamples, and the samples were then treated with 10 volume percent ofthe promoter solution used in Example 1. As in the previous examples,the treated naphthas were placed in storage vessels and the progress ofthe sweetening was followed over a period of time. The results obtainedare presented in Table III.

Table III COMPARISON OF SWEETENING RATES OF VIRGIN NAPHTHA AND CATALYTICNAPHTHA Table 1l Mercaptan Number 1 Naritha Naphtha B Naphthan CProcedure Used 1 2 3 3 4 Raw Naphtha 7. 96 11.1 11.1 20.1 20.1 AfterFirst Caustic Wash 2.- 2. 64 4. 6 4. 6 7. 8 7. 6 After Kerosene SpentCaustic Wash 2 2. 16 2. 95 2. 5 3. 9 4. 7 After 18 Hours Storage 0.360.49 0.12 After 24 Hours Storage 3. 30 Alter 48 Hours' Storaf'r` 0. 50Hours to Pass Doctor Test.- 24 18 18 18 24 after admitting air Procedure1Spent kerosene caustic not ecrated; 50 percent air sapce in holdingtank.

Procedure 2-Spent kerosene caustic aerated; 50 percent air space inholding tank.

Procedure -Spent kerosene caustic aerated; air excluded from holdingtank and naphtha blanketed with nitrogen.

Procedure 4-Speut kerosene caustic not aerated; air excluded tromholding tank during first 24 hou: period and then admitted.

1Mlligrams of mercnptan sulfur per 100 milliliters of naphtha.

l 10 volume percent of 15 Baume caustic used in each instance.

It will be noted from the first column of data in Table II thatsweetening of naphtha A was successfully accomplished without previouslyaerating the promoter solution, the air in the tank providing thenecessary oxygen for the sweetening. Comparison of the data of thesecond and third columns in the table indicates that the oxygen pickedup by the promoter solution during aeration was sufcient to effect thesweetening, since in the case where procedure 3 was followed, whereinair was excluded from the holding tank, sweetening was essentially asrapid as when following procedure 2 wherein a 50 percent air space wasprovided in the holding tank. Comparison of the data in the fourth andiifth columns of the table indicates that air must be introducedsomewhere in the system.

It will be noted, also that when procedure 4 was followed, Very littlesweetening occurred during the iirst 24 hours when the naphtha wasprotected from any air contact and the promoter solution had not beenaerated. After air was admitted to the tank at the end of the first 24hours storage, sweetening proceeded rapidly during the next 24 hours,even though no additional agitation was applied between the first andsecond 24 hour storage periods.

Other sweetening tests with naphthas of the general nature of Naphtha Aindicated that the sweetening reaction proceeds essentialy as rapidly at40 to 50 F. as at 75 to 77 F. when employing the procedures of thisinvention.

EXAMPLE 3 An additional set of tests was conducted to study sweeteningof virgin naphthas. For these tests a sour virgin naphtha having anA.P.I. gravity of 68.1 and a boiling Mercaptan Number Percent Virgin Nahtha. 5

0 Percent Catalytic aphtha Raw Naphtha After First Caustic Wash... AfterKerosene Caustic Wash.

After Hours Storage Hours to Pass Doctor Tes It will be noted from thedata obtained that the blend containing 25 percent of the virgin naphthasweetened as rapidly as the 100 percent catalytic naphtha and that ablend of 5-0 percent virgin naphtha and 50 percent catalytic naphtha wassweetened within a period of 18 to 24 hours. It is thus practical toadmix up to 50 percent of a sour virgin naphtha with the cracked naphthaand obtain the benefits of this invention. A blend containing 75 percentvirgin naphtha required from 48 to 72 hours for sweetening, whereas thesample of 100 percent virgin naphtha showed virtually no sweetening evenafter 120 hours.

It is to be understood that this invention is not to be limited by thespecic examples given nor by any theory regarding its operation. Thescope of the invention is defined by the following claims.

What is claimed is:

l. In a process for the sweetening of a sour petroleum distillatecontaining mercaptans, involving the oxidation of the mercaptans todisuliides, the improvement which comprises adding to the saiddistillate 0.05 to l pound of an inhibitor compound per thousand gallonsof distillate, said compound being selected from the class consisting ofamine, amide and phenol oxidation inhibitors, thereafter contacting thedistillate in the absence of substantial amounts of added free sulfurAwith a caustic solution previously employed for treating a raw kerosenefraction, separating said distillate from said caustic solution, andstoring the thus treated distillate for a period of at least severalhours to eiiect sweetening, said process including the step ofintroducing oxygen into said distillate subsequent to the addition ofsaid compound.

2. Improved process are defined by claim 1 wherein said introduction ofoxygen is effected by aerating the caustic from kerosene treating, priorto contact with the said distillate.

3. A process for sweetening a sour cracked naphtha which comprises thesteps of treating the naphtha in a irst zone with a caustic solution toremove caustic-soluble materials including hydrogen suliide andthiophenols, adding to the caustic-treated naphtha 0.05 to 1 pound of aninhibitor compound per thousand gallons of naphtha, said compound beingselected from the class consisting of amine, amide and phenol oxidationinhibitors, thereafter :treatngthe naphtha in the absence of substantialamounts Aof 'added free Vsulfur in a secondzonewitha caustic solu- 'tionpreviously employed for treating a :raw :kerosene fraction, separatingsaid naphtha from said caustic Vsoluytion-and storingthe Vthus treatednaphtha Vfor .aiperiod ,of 'at least severalhours to eectsweeteningsaidprocessin- `cluding the step of introducing oxygeninto said naphthaVsubsequent-to #the addition of the said compound.

A4. Process as defined by claim 3 wherein said -introduction of loxygenis effected by aerating the caustic from kerosene'treating, 'priortocontact with the said naphtha.

'5. Process as dened by claim 3 wherein the said added compoundcomprises a phenylene diamine.

6. Process as dened by claim 3 wherein'the compound comprises N,Ndisecbutyl `p-phenylene diamine.

7. Process as defined by claim 3 wherein said cracked .Bnaphthaisgadmxed withup'to 5.0zpercent of a sourvirgin :naphtha :8.Processias dened .by claim `wherein -said introduc- 'tion of 'oxygen iseffected .during fthe step :of rstoring 'the -said:naphtha.

`9. .Process .as defined by claim 3 wwherein said .caustic .employed fortreating said kerosene :fraction is of from 10 to 20 B. strength and isemployed'in thesproportion '.of from:5 1o 20 .volume percent ofthenaphtha.

References -Cited inthe le of this patent UNITED STATES PATENTS2,552,399 Browder 'May'8, 1951 '2,701,784 Cauley Feb. 8, 1955 y2,771,403-Kalinowski et a'l NOv.'2U, 1956 l27812.96 Brown `Feb. '12, 1957

1. IN A PROCESS FOR THE SWEETENING OF A SOUR PETROLEUM DISTILLATECONTAINING MERCAPTANS, INVOLVING THE OXIDATION OF THE MERCAPTANS TODISULFIDES, THE IMPROVEMENT WHICH COMPRISES ADDING TO THE SAIDDISTILLATE 0.05 TO 1 POUND OF AN INHIBITOR COMPOUND PER THOUSAND GALLONSOF DISTILLATE, SAID COMPOUND BEING SELECTED FROM THE CLASS CONSISTING OFAMINE, AMIDE AND PHENOL OXIDATION INHIBITOR, THEREAFTER CONTACTING THEDISTILLATE IN THE ABSENCE OF SUBSTANTIAL AMOUNTS OF ADDED FREE SULFURWITH A CAUSTIC SOLUTION PREVIOUSLY EMPLOYED FOR TREATING A RAW KEROSENEFRACTION. SEPARATING SAID DISTILLATE FROM SAID CAUSTIC SOLUTION, ANDSTORING THE THUS TREATED DISTILLATE FOR A PERIOD OF AT LEAST SEVERALHOURS TO EFFECT SWEETENING, SAID PROCESS INCLUDING THE STEP OFINTRODUCING OXYGEN INTO SAID DISTILLATE SUBSEQUENT TO THE ADDITION OFSAID COMPOUND.